There is a need for systems to rapidly identify markers of protective immunity against a number of category A, B and C agents of high public and international health importance. In addition, there is a need for the development of platforms to rapidly evaluate the breadth and duration of immune responses following vaccination against such pathogens, correlating responses to those found to be protective. Vibrio cholerae is a category B agent, and the cause of cholera, a secretary diarrhea that results in significant morbidity and mortality worldwide. The mediators of protective immunity against cholera are poorly understood, and although a number of cholera vaccines have been developed, each has significant limitations. We propose to use previously created reagents (already-collected clinical specimens and already-produced V. cholerae NAPPA protein microarrays) to perform high throughput proteomics-based screening to identify markers of protective immunity against cholera, and to compare immune responses correlating with protection with those induced following vaccination. To do this, we propose a cooperative research partnership between researchers at the Massachusetts General Hospital (MGH), Harvard Institute of Proteomics (HIP), and International Centre for Diarrheal Disease Research in Dhaka, Bangladesh (ICDDR,B). Specific Aim #1. Use NAPPA to screen serum of household contacts of cholera index patients, stratifying responses by level of protection from cholera. Purify antigens of interest, and confirm immune responses. Specific Aim #2. Use NAPPA to screen antibody-in-lymphocyte supernatants of memory B cells of household contacts of cholera index patients, stratifying responses by level of protection from cholera. Purify antigens of interest, and confirm immune responses. Specific Aim #3. Use NAPPA to screen serum of vaccines who have received killed oral whole cell cholera vaccine (WC-rBS) or live oral attenuated cholera vaccine Peru-15, comparing immunoproteomic responses to those correlating with protection from cholera. The major objective of this project is to identify and purify V. cholerae immunogens against which immunoreactivity in humans corresponds with protection from cholera. These immunogens would subsequently be evaluated for inclusion in subunit cholera vaccines or boosters.